As a conventional technique, a displacement detection device for detecting a displacement of a needle of an injector has been proposed (see, for example, Patent Literature 1).
The displacement detection device disclosed in Patent Literature 1 is a lift sensor that is provided inside an injector body of the injector and detects the displacement of the needle. The injector includes an injector body having a fuel passage therein, a needle provided in the passage of the injector body, and a solenoid coil applying force to push and pull the needle, and a tip portion of the needle comes in contact with a seam near a fuel nozzle hole on an inner wall of the injector body to close the nozzle hole and separates from the seam to open the nozzle hole. The displacement detection device has a sensor plate that moves together with the needle and a gap sensor that detects a gap between the gap sensor and the sensor plate, and detects the displacement of the needle by detecting the gap with the sensor plate by the gap sensor.